Eccentric muscle damage increases intermuscular coherence during a fatiguing isometric contraction

Aim: The purpose of this study was to determine the effect of eccentric muscle damage on muscle activation patterns and intermuscular coherence during a fatiguing isometric contraction involving the elbow flexor muscles. Methods: Ten young subjects participated in three experimental sessions that involved the performance of maximum voluntary contractions (MVCs), a constant-force task at 30% MVC, and a fatiguing isometric contraction at 30% MVC. The three sessions were performed before, 2h after and 2days after eccentric exercise to induce muscle damage in elbow flexor muscles. Task performance was quantified with electromyography (EMG) from the elbow flexor (biceps brachii, brachialis and brachioradialis) and extensor (triceps brachii) muscles, M-wave amplitude of biceps brachii, elbow flexor force fluctuations and endurance time of a fatiguing contraction. Intermuscular coherence during the fatiguing contraction was quantified from the rectified surface EMGs between muscle pairs. Results: Eccentric exercise resulted in several indicators of muscle damage, such as a prolonged decline in muscle strength and an increase in muscle soreness 2days after exercise. A 29% reduction in endurance time was observed 2h after eccentric muscle damage, which returned to baseline 2days later. The reduced endurance time 2h after muscle damage was accompanied by an increase in EMG-EMG coherence between biceps brachii and brachialis muscles, which was observed at the end of the fatiguing contraction. Conclusion: These findings suggest that eccentric muscle damage produces a decrease in endurance time that is accompanied by an increase in intermuscular coherence in the presence of fatigue.